There are numerous multi-step, sequential-step, and more recently, single-step methods that have been disclosed in the literature to prevent the leaching of metals from solids, semi-solids, liquids and/or gaseous complex matrices contained in FGD wastes. If stabilized properly, the FGD waste can be rendered suitable for disposal in a sanitary landfill.
Douglas U.S. Pat. No. 4,671,882 discloses a multi-step process for heavy metal stabilization. Douglas does not prefer to use limestone. According to Douglas, the use of limestone results in the production of carbon dioxide gas when added to acid solution. This carbon dioxide would adversely affect the pH-increasing step essential to Douglas's multi-step heavy metal stabilization process.
Stanforth U.S. Pat. Nos. 4,889,640 and 5,037,479 suggest that limestone is not as effective in the disclosed heavy metal stabilization processes because it is a nonreactive form of calcium and/or magnesium carbonate.
Bhat U.S. Pat. Nos. 5,719,099; 5,985,778; 6,191,068; 6,313,368; and, 6,388,165 all disclose various single step and/or single products or methods for stabilization of heavy metals, acid gas removal and pH control in various contaminated matrices. The compositions comprise various combinations of phosphate-, aluminum-, and alkali-containing materials. Of the seventeen metals tested by Bhat in the referenced patents, all rated “fair” or “poor” in stabilizing two of the metals—Arsenic (As) and Selenium (Se).
The disclosures of all of the above references are hereby incorporated herein by reference. This listing is not intended to be a representation that a complete search of all relevant art has been made, or that no more pertinent art than that listed exists, or that the listed art is material to patentability. Nor should any such representation be inferred.